In a labyrinthine district of New Delhi, Kalpana Singh is busy knocking on doors, straining to make out house numbers scratched on the walls and warmly greeting residents with a smile.
She is on a mission to record and document the occupants of the teeming and decrepit area in a routine being repeated daily across the chaotic country as part of the 2011 national census.
The scale of the task is vast, the complications enormous and the effort and patience required in the summer heat of over 40 degrees Celsius (104 degrees Fahrenheit) admirable.
The census, undertaken every decade since 1872, will see 2.5 million staff fan out over a country with a bewildering range of cultures, languages and customs, rebel movements and at least 600,000 villages.
Kalpana, a teacher recruited for the exercise, has been given a mainly Muslim area of New Delhi in the north of the city, with 100 buildings and approximately 400 households. Two local adolescents serve as guides.
"Do you have toilets? A mobile phone? a bank account? Which caste are you from?", the same questions are repeated over and over again at each house.
The one on caste was a controversial late addition when the government bowed to opposition pressure for it to be included for the first time since the British colonial era in 1931.
Many have opposed the idea of recording information on the rigid Hindu caste system, a vexed subject that the country is unable to leave behind. Bollywood legend Amitabh Bachchan is outraged, saying he is "Indian" and nothing more.
The census records a range of information, designed to give a picture of the economic and social development of the country since the last national survey in 2001, when the population was just over a billion.
In Kalpana's area, most people have toilets, running water and electricity, though not all of the time. Many have a mobile phone, some have a computer with Internet access but very few have bank accounts. Cars are unknown.
The difficulty lies in obtaining accurate information and ensuring that everyone who lives at an address is accounted for.
In one home, a young man of about 30 afflicted by polio answers the door and invites Kalpana in to his windowless room of four square meters (43 square feet).
She begins explaining the process, but as her eyes adjust to the dark she notices a hole in the ceiling and a ladder. In fact, eight people live here, sleeping between the floors.
Many people are unsure of their age. In one instance, a veiled woman sitting in front of her house has to go to check her details on an official document. Others tend to round up or down to the nearest decade.
Enumerators like Kalpana had only three days of training in how to fill in the boxes and get people to cooperate, which she appears to be putting to good effect, while others seem not to have grasped the basics.
One colleague tells her he is only taking names down without asking other questions.
"It is a challenge to see that the 2.5 million enumerators carry out the instructions we have given them without error," census commissioner C. Chandramouli told AFP in an interview earlier this year.
"The trick is to get things right the first time. There is no question of a re-census."
The margin for error in 2001 was estimated at 2.3 percent and this year organisers hope to improve.
But there is added organisational complexity this time because after the physical count of people, another official will visit each house to gather biometric data for the first time -- digital fingerprints and eye scans.
Everyone will also be photographed as part of efforts to roll out individual 16-digit Unique Identity Numbers nationwide which will serve as a one-stop proof for all Indians to establish their identity.
Kalpana's boss, Reena Sharma, says she is proud of her work as she sits on the terrace of a decrepit building, asking a grandmother about the 13 members of her family.
"It's a good experience. We have the privilege of doing this work. We're doing something for the nation," she said.